Which part is not necessary to complete a circuit

An electron in an x-ray machine is accelerated through a potential difference of 1.00 × 104 v before it hits the target. what is the kinetic energy of the electron in electron volts?

Coal contains energy. a. light b. kinetic c. chemical d. mechanical

Calculate a pendulums frequency of oscillation (in hz) if the pendulum completes one cycle in 0.5s.